1. Field of the Invention
The present invention relates to a steering system for vehicles of the type in which a rear wheels is steerable in relation to the steering operation of a front wheel.
2. Description of Relevant Art
There has already been proposed a steering system for vehicles in which a rear wheel is steerable in relation to the steering of a front wheel such that the steered angle ratio of the rear wheel to the front wheel is variable in accordance with the vehicle speed. (Japanese Laid Open Application JP-A-59-26363 dated Feb. 10, 1984)
More particularly, in such proposed steering system, the rear wheel is steered, at relatively low vehicle speeds, in the opposite direction to the front wheel or substantially by zero degree and, at relatively high vehicle speeds, in the same direction as the front wheel. The steered angle ratio is given as a continuous function of the vehicle speed, as represented by a curve X shown in FIG. 7 of the accompanying drawings, such that for vehicle speeds higher relative to a predetermined vehicle speed d.sub.1 the angle ratio is positive, that is, the front and rear steered angles are the same in phase, and for vehicle speeds lower relative thereto the angle ratio is negative, that is, the steered angles are opposite in phase, whereby continuous control of the steered angle ratio is achieved to be effected along the function curve X, ranging from a low speed to a high speed. As a result, at relatively low vehicle speeds, the minimum turning radius of the vehicle as well as the inside wheel span is remarkably reduced, in addition to favorable facilitation of the vehicle turning characteristics such as when parking, travelling along a narrow curved road, and making a U-turn. Moreover, at relatively high vehicle speeds, the steering responsiveness can be highly improved.
In a low speed range, however, there often occurs a case in which the handling operation is facilitated by steering a rear wheel in the same direction as a front wheel rather than steering same in the opposite direction thereto, such as when parallel parking the vehicle in a row of longitudinally parked cars or maneuvering the vehicle relative to laterally approaching neighboring objects.
With such view in mind, the present invention has been achieved to provide an improvement in a steering system for vehicles of the above-mentioned type.